Thermal trip unit with calibrating adjustment



y 3, 1966 c. E. GRYCTKO ET AL 3,249,720

THERMAL TRIP UNIT WITH CALIBRATING ADJUSTMENT Filed Feb. 19, 1962 4 Sheets-Sheet 1 y 3, 1966 c. E. GRYCTKO ET AL 3,249,720

THERMAL TRIP UNIT WITH CALIBRATING ADJUSTMENT Filed Feb. 19, 1962 4 Sheets-Sheet 2 y 3, 1966 c. E. GRYCTKO ET AL 3,249,720

THERMAL TRIP UNIT WITH CALIBRATING ADJUSTMENT Filed Feb. 19, 1962 4 Sheets-Sheet 3 THERMAL TRIP UNIT WITH CALIBRATING ADJUSTMENT y 1966 c. E. GRYCTKO ET'AL 4 Sheets-Sheet 4 Filed Feb.

United States Patent 3,249,720 THERMAL TRIP UNIT WITH CALIBRATING ADJUSTMENT Carl E. Gryctko, Haddon Heights, N.J., and Martin V.

Zuhaty, Philadelphia, Pa., assignors to I-T-E Circuit Breaker Company, Philadelphia, Pa., a corporation of Pennsylvania Filed Feb. 19, 1962, Ser. No. 174,057

16 Claims. (Cl. 200-122) This invention relates to circuit breakers in general and more particularly to a thermal trip unit for a multi-phase circuit breaker.

Presently, most multi-phase circuit breakers are constructed such that if a current fault condition should occur in any phase, this will bring about automatic opening of all phases. For the most part, fault detection brings about automatic tripping either on a so-called, instantaneously or on-a time delay basis.

Time delay tripping is controlled by the action of a bimetallic element heated by energy which is a function of the current flowing through the particular phase of the circuit breaker with which the bimetal is associated. An individual bimetal is provided for each phase of the circuit breaker with the bimetal acting to operate a tripper bar common to all phases.

In prior art circuit breakers of this type calibration means for the time delay tripping means usually consisted of screws mounted directly on the tripper bar or on the bimetal itself. During the calibration process, adjustment of the screw often applies additional load to the tripping means. This introduces an uncontrolled load resulting in inaccuracy so that inconsistent results are obtained from the trip unit. Also, calibration varies due to changes in tripper bar loads or in calibrating forces.

Further, prior art calibration of the thermal trip device is usual-1y carried out with the circuit breaker cover removed so that the thermal elements are exposed to external air currents during the calibration process. When the circuit breaker is installed in the field and its cover is in place, the thermal elements are not exposed to external air currents so that the calibration previously made is unreliable.

The instant invention overcomes all of the difliculties ,of similar prior art devices by providing an automatic trip unit construction in which calibration is accomplished .while the circuit breaker cover is in place and calibration does not place any load upon the bimetal or the tripper bar. This is accomplished by providing a bimetal which is mounted to a distortable heater member. One end of the bimetal is deflectable into engagement with the circuit breaker tripper bar for operation thereof. Spacing between the free end of the bimetal and the tripper bar is adjusted by distorting the heater member.

The heater member includes agenerally rectangular port-ion with the bimetal being mounted to one of the long sides of the rectangle. An adjusting screw extends across the central portion of the rectangle and is in operative engagement with the side upon which the bimetal is mounted. The adjusting screw is also in threaded engagement with the side of the rectangle opposed to the side upon which the bimetal is mounted. Operation of the adjusting screw is effective to distort the heater .memher and thereby reposition thefree end of the bimetal. The adjusting screw is accessible for operation with the circuit breaker cover in place.

Accordingly a primary object of the instant invention is to provide a novel construction for the thermal trip unit of a circuit breaker.

Another object is to provide a trip unit of this type which is adjustable while the circuit breaker cover in place.

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Still another object is to provide a trip unit of this type in which calibration is accomplished without applying additional load to either the bimetal or the tripper bar.

A further object is to provide a trip unit of this type in which the bimetal is mounted directly to its heater element.

These as well as other objects of this invention shall become readily apparent after reading the following description of the accompanying drawings in which:

FIGURE lis a plan view of a circuit breaker including the device of the instant invention.

FIGURE 2 is a cross-section taken through line 2--2 of FIGURE 1 looking in the direction of arrows 2-2.

'FIGURE 3 is an exploded perspective of an automatic trip unit constructed in accordance with the teachings of the instant invention.

FIGURE 4 is a cross-section of the automatic trip unit taken through line 44 of FIGURE 5 looking in the direction of arrows 4- -4.

FIGURES 5 and 6 are end views of the trip unit looking in the direction of arrows 55 and 66, respectively of FIGURE 4.

FIGURE 7 is a cross-section taken through line 7-7 of FIGURE 4 looking in the direction of arrows 77. 7

FIGURE 8 is a cross-section taken throughline 88 of FIGURE 7 looking in the direction of arrows 88.

FIGURE 9 is a plan view illustrating the manner in which the instantaneous trip means biasing spring engages the armature.

' Now referring to the figures. Circuit breaker 15 is provided with a molded housing comprising base 16 and removable cover 17. Base 16 is divided into three longitudinal compartments by partitions 18, 19. The center compartment houses contact operating mechanism 20 of a type well known to the art which is effective to simultaneously operate cooperating contacts 21, 22 of both circuit breaker poles into and out of engagement.

' Circuit breaker 15 is a two pole device with the current carrying elements of the respective poles being housed in the outer compartments of base 16. The current carrying elements as well as the automatic trip device of each pole are the same. The current path for each pole comprises terminal strap 23, stationary contact 22, movable contact 21, movable contact arm element 24, flexible braid 2 5, strap 26, bimetal heater element 30 to terminal strap 31.

Movable contact arm element 24 is pivotally mounted at 32 to contact arm element 33 with contact pressure spring 34 being interposed between'elements 24 and 33 to provide contact pressure. Elements 33 of both poles are fixedly secured to cross bar 35 which is operated by mechanism 20 to bring about simultaneous opening and closing of contacts 21, 22 of both poles. Circuit breaker 15 also includes common tripper bar 36 biased to latching position (arrow A, FIGURE 2) in a manner well known to the art.

In order to bring about automatic tripping of circuit breaker 15, each of the poles is provided with an automatic trip unit 46 including bimetal 39 and armature 38 which is attracted to the pole piece 37 of an electromagnet. So-called intantaneous tripping takes place when armature 38 is attracted by pole piece 37 and moves in the direction of arrow B (FIGURE 2) and in so doing engages tripper bar extension 41, thereby rotating tripper bar 36 in the direction opposite to the direction of arrow A. So-called time delayed tripping takes place when the upper or free end of bimetal 39 moves in the direction of arrow C (FIGURE 2) thereby engaging tripper bar extension 42 to operate tripper bar 36 in a direction opposite to the direction indicated by arrow A. Birnetal heater element 30 is of generally rectangular shape having elongated opposite sides 43, 44. The upper ends of sides 43, 44 are bridged by side 45 while side 46 extends from the lower end of side 43 but stops short of side 44. Side 46 is provided with clearance aperture 47 which receives mounting screw 48. The lower end, of side 44 is provided with leg 49 extending away from side 43. Leg 49 is provided with clearance aperture 50 which receives mounting screw 51.

As clearly seen in FIGURES 3 and 6, side 44 is considerably narrower than sides 43, 45 and 46 so that most of the heating takes place at side 44.. The lower end of bimetal 39 is secured to the downward extension 52, of side 44, which is formed from extension 49. The threads of adjusting screw 53 are mated with the threads of aperture 54 through side 43. End 55 of screw 53 is provided with a suitably formed recess to receive an adjusting tool such as an Allen wrench while the other end of screw 53 is provided with a portion 56 of reduced cross section having an enlargement 57 at the free-end thereof. Shoulder 58, adjacent to portion 56, abuts the inner surface of side 44 with portion 56 extending through clearance aperture 59 of side 44 and spring retainer 60 being interposed between enlargement 57 and the outside surface of side 44.

As adjusting screw 53 is rotated clockwise, a force is directed to increase the spacing between the central portions of walls 43 and 44. This re-positions the extension 52 of wall 44 thereby bringing the free end of himetal 39 closer to tripper bar extension 42 thereby decreasing the delay tripping time of circuit breaker Conversely, rotation of screw 53 in a counterclockwise direction will increase the spacing between the free end of bimetal 39 and tripper bar extension 42 thereby increasing the time delay tripping interval for circuit breaker 15. It is noted that end 55 of adjusting screw 53 is made accessible with the cover 17 of circuit breaker 15 in place merely by removing cover strip 62 which is disposed within slotted formation of base 16.

Pole piece 37 is a generally U-shaped member provided with pole faces 64, 65 which lie in a common plane. Pole piece 37 is nested within U-shaped retainer slip 66 with outward projections 67 of the pole piece U-arms disposed within apertures 68 in the U-arms of retainer clip 66. The web of pole piece 37 is provided with clearance aperture 69 while the web of the retainer clip 66 is provided with clearance aperture 70. Apertures 69 and 70 are aligned with aperture 47 of heater side 46 so that screw 48 extends through all three elements and constitutes a common fastening means.

The U-arms of retainer element 66 each include portions extending beyond pole faces 64, 65. These portions are provided with aligned apertures 71, 72 which receive outboard extensions 73, 74, respectively of armature 38 thereby defining a pivotal axis for armature 38. These portions of retainer clip 66 also include enlarged apertures 75, 76 which receive outboard extensions '77, 78, respectively, of armature 38. Apertures 75, 76 are considerably larger than extensions 77, 78 thereby permitting armature 38 to pivot toward and away from pole faces 64, 65.

Each of the U-arms of pole piece 37 is provided with an under cut portion 79 while armature 38 is provided with two sets of indentations 90. Somewhat V-shaped compress-ion leaf spring 91 is interposed between pole piece 37 and armature 38 thereby urging armature 38 away from pole faces 64, 65. Each end of spring 91 is notched to provide a pair of closely spaced tips 92. Tips 92 at one end of spring 91 are received by one of the sets of notches 99 while the tips 92 at the other end of spring 91 are disposed on opposite sides of under cut 79 thereby Further, this force is regulated by the characteristics and dimensions of the spring material. It is noted that retainer clip 66 is constructed of non-magnetic resilient sheet material so that no additional fastening means are required to secure pole piece 37, armature 38 and retainer clip 66 together as a unit. Further, the mounting of pressure spring 91 is extremely simple and does not require the permanent deformation of any element.

Although preferred embodiments of this novel invention are described herein, many variations and modifications will now be apparent to those skilled in the art and, therefore, it is preferred that this invention be limited not by the specific disclosure herein but only by the appending claims.

The embodiments of the invention in which an exclusive privilege or property is claimed are defined as follows:

1. A thermal trip device for a circuit breaker, said device comprising a member including first and second opposed sides and a third side joining said first and second sides at their respective first ends, an elongated bimetal element extending along said first side and mounted at one of its ends to said first side at its second end, adjusting means operatively interconnecting sai-d sides for distorting said first side, the distortion of said first side controllably repositioning the other end of said bimetal to a selected position relative to a circuit breaker tripper element.

2. The thermal trip device of claim 1 in which the ad-- justing means comprises a screw in threaded engagement with one of said first and said second sides at an intermediate region thereof. 4 3. The thermal trip device of claim 2 in which the screw includes a non-threaded portion; the other of said first and said second sides including a clearance aperture; said non-threaded portion being disposed in said clearance aperture.

4. The thermal trip device of claim 3 in which the member also includes a fouith side opposed to said third side, said fourth side extending from said second side at its second end, said fourth side being provided with means for mounting said device to a circuit breaker base.

5. The thermal trip device of claim 1 in which said first side is of reduced cross-section and constitutes a heater for the bimetal.

6. A multi-p'hase circuit breaker including a pair of cooperating contacts for each phase; a mechanism for simultaneously operating said contacts of all phases between an engaged and a disengaged position; a common tripper bar which when operated to a trip position enables said mechanism to automatically operate said pairs of contacts of all phases to said disengaged position; a thermal trip device for each of said phases; each of said trip devices comprising a member including first and second opposed sides and athird sidejoining said first and second sides at their respective first ends, an elongated bimetal element extending along said first side and mounted at one of its ends to said first side at its second end, adjust ing means operatively interconnecting said sides for distorting said first side; the distortion of said first side con trollably repositioning the other end of said bimetal to a selected position relative to said common tripper bar whereby a predetermined overload condition will cause deflection of the other end of said bimetal sufficient to operate said tripper bar to said trip position.

7. The circuit breaker of claim 6 in which the adjusting means of each phase comprises a screw in threaded engagement with one of said first and said second sides at an intermediate region thereof.

8. The circuit breaker of claim 7 in which each of said screws includes a non-threaded portion, the other of said first and said second sides including a clearance aperture; said non-threaded portion being disposed in said clearance aperture.

9. The circuit breaker of claim 8 in which each of said members also includes a fourth side opposed to said third side, said fourth side extending from said second side at its second end, said fourth side being provided with means for mounting said device to a base for said circuit breaker.

10. The circuit breaker of claim 6 in which each of said first sides is of reduced cross-section and constitutes a heater for the bimetal.

11. The circuit breaker of claim 6, further including means connecting said adjustment means to said member in mechanical load isolation relationship with respect to said bimetal and said tripper bar 12. The circuit breaker of claim 6, further including housing means substantially enclosing said multi-phase circuit breaker; said housing means including access means externally communicating with said adjusting means.

13. A thermal trip arrangement for a circuit breaker, comprising an elongated bimetal element; bimetal support means including space separated first and second sides and a third side joining said first and second sides at their respective first ends; said bimetal extending along said first side; means mounting a first end of said bimetal to said first side; adjusting means engaging intermediate opposed regions of said first and second sides to predeterminedly vary the extent of said space separation; said variation predeterminedly relocating a second end of said bimetal to effect calibration :thereof relative to a circuit breaker tripper element.

14. A thermal trip arrangement as set forth in claim 13, further including means connecting said adjustment means to said support means in mechanical load isolation relationship relative to said bimetal.

15. A thermal trip arrangement as set forth in claim 13, wherein said adjusting means comprises a screw in threaded engagement with one of said first and second sides; said screw including a non-threaded portion disposed within a clearance aperture of the other of said first and second sides.

16. A thermal trip arrangement as set forth in claim 15, wherein said screw includes externally accessible means for relatively varying the length of said screw intermediate said opposed first and second surfaces; said variation in length providing said predetermined variation in said space separation for unit calibration.

References Cited by the Examiner UNITED STATES PATENTS 3,023,28-8 2/1962 Bodenschatz et al. 200-122 X 3,061,697 10/1962 Kralik et at 200-88 KATHLEEN H. CLAFFY, Primary Examiner.

ROBERT K. SCHAEFER, Examiner.

M. GINSBURG, Assistant Examiner. 

1. A THERMAL TRIP DEVICE FOR A CIRCUIT BREAKER, SAID DEVICE COMPRISING A MEMBER INCLUDING FIRST AND SECOND OPPOSED SIDES AND A THIRD SIDE JOINING SAID FIRST AND SECOND SIDES AT THEIR RESPECTIVE FIRST ENDS, AN ELONGATED BIMETAL ELEMENT EXTENDING ALONG SAID FIRST SIDE AND MOUNTED AT ONE OF ITS ENDS TO SAID FIRST SIDE AT ITS SECOND END, ADJUSTING MEANS OPERATIVELY INTERCONNECTING SAID SIDES FOR DISTORTING SAID FIRST SIDE, THE DISTORTION OF SAID FIRST SIDE CONTROLLABLY REPOSITIONING THE OTHER END OF SAID BIMETAL TO A SELECTED POSITION RELATIVE TO A CIRCUIT BREAKER TRIPPER ELEMENT. 